The primary goal of this program of research is to extend our understanding of the role that stressful life events and personality characteristics play in susceptibility to infectious agents. The work includes a replication of our earlier work showing a dose-response relation between psychological stress and illness susceptibility, but also extends this work by attempting to identify (a) the objective characteristics of stressful life events that place people at risk for infectious disease; (b) the temporal relations between life event occurrence and increased susceptibility; (c) the psychological, behavioral, and biological pathways linking life events to illness susceptibility; and (d) the role of personality characteristics in directly influencing disease susceptibility or in moderating stressor-susceptibility relations. To accomplish these goals we use a unique human upper respiratory disease model that allows us the ability to experimentally control exposure to a virus and to monitor the development of both infection and clinical illness. We expect that evidence from this study will provide strong clues as to the psychosocial, endocrine, and immune characteristics that play a role in susceptibility to HIV infection and in triggering the onset of AIDS among HIV-infected persons. Over a three year period, 300 healthy volunteers will participate in this prospective study. Prior to viral-challenge subjects will complete psychological, neuroendocrine, immunological, and health practice assessments. Most of these measures will be assessed twice with a 7 day interval to assure reliable characterization of subject status. Psychological measures include a semi-structured life events interview, a life events check list, a perceived stress questionnaire, measures of state and trait affectivity, and of the "big" five factors that are thought to represent the totality of personality. Neuroendocrine measures include 24-hour urine catecholamines and cortisol. Immune measures include natural killer cell numbers and activity and lymphocyte production of interferon-alpha and -gamma. Finally health practice measures include assessments of smoking status and rate, alcohol consumption, diet, exercise, and sleep quality. After the assessment procedure is completed, subjects will be exposed by nasal drops to one of two rhinoviruses, quarantined and monitored for infection and symptoms for six days. We collect symptom interviews, nasal washings for detection of viral shedding, and objective measures of pathophysiology (temperature, mucus weights, nasal clearance, nasal congestion, presence of inflammatory mediators) before viral-challenge and on each of the 6 days after challenge. The primary outcomes in the study are infection (virus shedding or increase in viral-specific antibody) and clinical illness (infection + clinical diagnosis).